Installation for Water Treatment by Flotation and Corresponding Water Treatment Method

ABSTRACT

The invention relates to a flotation water treatment plant comprising at least: an inlet zone ( 31 ) for the water to be treated, which is coagulated and flocculated beforehand; a mixing zone ( 32 ), for mixing pressurized and then depressurized water with said water to be treated; a flotation zone ( 35 ) separated from said mixing zone by a wall; a clarified-water take-up zone ( 36 ) provided in the lower part of said flotation zone ( 35 ). According to the technique shown here, said mixing zone accommodates ( 32 ) at least one spray nozzle ( 40, 91, 92 ) for spraying said pressurized water, said spray nozzle ( 40, 91, 92 ) lying close to a panel ( 33 ), at least part of which has perforations ( 331 ), said panel separating said inlet zone ( 31 ) from said mixing zone ( 32 ).

FIELD

The field of the invention is that of clarification installations forthe treatment of water.

More precisely, the invention relates to installations for waterclarification that use the flotation method.

PRIOR ART

An installation for water clarification by flotation according to theprior art is shown in FIG. 1.

Such clarification installation comprises a coagulation zone and aflocculation zone (not shown). In the coagulation zone, one or severalcoagulating agents (for example aluminium polychloride, aluminiumsulfate, iron chloride, etc.) are injected into the water to be treatedbefore the water is directed towards the flocculation zone.

Flocculation is a physical-chemical step which aims to modify the stateof the colloidal particles in suspension in the water in such a way thatthe particles coagulate with one another.

Such as shown in FIG. 1, such an installation for clarification byflotation comprises a mixing zone 1 in the lower part wherein areadmitted, in an ascending current, the water to be treated which iscoagulated and flocculated beforehand (arrow A), and a pressurised andthen depressurised water (arrow B) in such a way that micro air bubblesare formed. Such as shown by the arrow C, the air bubbles thus formedmake it possible to bring towards the surface of the mixing zone all ofthe particles in suspension in the water to be treated agglomerated tothe air bubbles. The mixture of particles agglomerated to the airbubbles forms a bed of bubbles 2 which extends at the surface of themixing zone 1 and flotation zone 3.

These particles agglomerated to the air bubbles can then be removed(arrow D) in the upper part of the flotation zone 3.

The taking up of clarified water is carried out in the lower part of theflotation zone 3 for example by means of perforated piping 4 connectedto conduits 5, or to any other means.

DISADVANTAGES OF PRIOR ART

A disadvantage of this technique of prior art is linked to the design ofthe mixing zone. Indeed, this mixing zone does not allow for homogenouscontact of the water to be treated, which is coagulated and flocculatedbeforehand, and of the pressurised and then depressurised water acrossthe entire horizontal section of the mixing zone. This lack ofhomogenous contact is observed regardless of the value of the flow rateof the water to be treated, the quality of the water to be treated, andthe value of the flow rate of the pressurised and then depressurisedwater.

Such a lack of homogenous contact generally results in disturbing thephenomenon of agglomeration of particles in suspension in the water tobe treated with the micro air bubbles, which tends to reduce theeffectiveness of the treatment of the water.

Another disadvantage of this technique of prior art is linked to thedesign of the flotation zone. Indeed, the matter in suspensionagglomerated to the air bubbles is driven by a recirculation loopphenomenon, to the clarified-water take-up zone.

Such a phenomenon can therefore generate the departure of matter insuspension agglomerated to the micro bubbles into the flow of clarifiedwater. Consequently, the clarified water collected contains impuritiesand the effectiveness of the device is therefore affected.

Furthermore, the bed of matter in suspension agglomerated to the airbubbles, which forms on the surface of the flotation zone, can reach aheight close to the height of the flotation zone, which, associated withthe recirculation phenomenon, favours the departure of impuritiestowards the clarified-water take-up zone.

This recirculation phenomenon is shown in FIG. 2 wherein are shown thespeed vectors 21 of the flow of the water contained in the flotationzone are shown. It can be seen in this FIG. 2 that the clarified waterhas a tendency to rise towards the top of the flotation zone where thebed of air bubbles is located. The clarified water then mixes with themicro air bubbles loaded with particles initially in suspension in thewater to be treated before being redirected towards the bottom of theflotation zone.

OBJECTIVES OF THE INVENTION

The invention in particular has for objective to overcome thesedisadvantages of prior art.

More precisely, an objective of the invention is to provide a techniquefor treating water that makes it possible to optimise the clarificationof water by flotation.

Another objective of the invention is to provide a technique for theclarification of water by flotation which makes it possible to obtain ahomogenous mixture of the water to be treated and of the pressurised andthen depressurised water.

The invention also has for objective to implement such a technique whichmakes it possible to prevent the appearance of recirculation phenomenonin the clarified-water take-up zone.

Another objective of the invention is to provide such a technique thatis reliable, simple and inexpensive to implement.

DESCRIPTION OF THE INVENTION

The invention relates to an installation for water treatment byflotation comprising at least:

-   -   one inlet zone of the water to be treated which is coagulated        and flocculated beforehand;    -   one mixing zone of a pressurised and then depressurised water        with said water to be treated;    -   one flotation zone separated from said mixing zone by a wall;    -   one clarified-water take-up zone provided in the lower part of        said flotation zone.

According to the invention, said mixing zone accommodates at least onespray nozzle of said pressurised water, said spray nozzle extending inthe vicinity of a panel, of which at least one portion has perforations,and which separates said inlet zone and said mixing zone.

Thus, the invention consists in interposing a perforated panel betweenthe inlet zone of the water to be treated and the mixing zone. Thepassage of the water to be treated through the perforated panel makes itpossible to homogenise and to fragment the flow of the water to betreated. This contributes to homogenize the contact between the water tobe treated and the micro air bubbles formed in the mixing zone by theintroduction of pressurised and then depressurised water over the entirehorizontal section of the mixing zone, which makes it possible toimprove the agglomeration of particles in suspension in the water to betreated with the micro air bubbles.

The invention makes it possible, moreover, to neutralise the hydraulicshort circuits, responsible for a loss in effectiveness by the lack ofcontact between particles in suspension and air bubbles.

The implementation of such a perforated panel according to the inventiontherefore makes it possible to optimise the treatment of the water byflotation and to consequently improve the quality of the clarified watercollected at the end of the treatment.

According to an advantageous characteristic, said panel extendssubstantially horizontally.

In this case, the flow of water to be treated is substantially ascendingdownstream of the panel. If the flocs formed during thecoagulation/flocculation are resistant, the pressurised water ispreferentially sprayed counter-current to the water to be treated. Thespray nozzles then extend substantially vertically in such a way thatthe pressurised water is sprayed according to an initially descendingcurrent.

If the flocs formed are fragile, the nozzles are placed in such a waythat the pressurised water is sprayed co-current to the water to betreated, i.e. in such a way that the pressurised water is sprayedaccording to an initially ascending current.

According to another advantageous characteristic, said panel extendssubstantially vertically.

In this case, the spray nozzles extend substantially horizontally insuch a way that the pressurised water is sprayed according to aninitially horizontal current. Only the direction of the spray isdifferent (co-current or counter-current) according to whether the flocsare fragile or resistant.

In other advantageous alternatives, it can be provided that the panel beinclined.

According to a preferred embodiment, a water treatment installationaccording to the invention comprises a plate forming a splash boardsubstantially parallel to said panel that extends between said panel andsaid nozzle and of which at least one portion has first holes.

The implementation of such a plate forming a splash board makes itpossible to improve the fragmentation of the flow of water to be treatedand thus to homogenise the contact between the micro air bubbles and thewater to be treated in the mixing zone.

Preferentially, said first holes of said plate extend in the extensionof solid parts of said panel.

This allows for the creation of baffles that must be crossed by thewater to be treated before it arrives in the mixing zone. The presenceof these baffles also makes it possible to improve the fragmentation ofthe flow of the water to be treated.

Advantageously, said plate has second holes which extend above saidperforations of said panel.

These second holes, also called holes or refining holes, make itpossible to optimise the homogenisation of the flow of water to betreated.

According to a preferred aspect of the technique shown here, each one ofsaid spray nozzles is placed substantially in the axis of one of saidperforations of said panel.

This makes it possible to obtain an optimal mixture between the flows ofwater to be treated and pressurised water. However, according to analternative wherein the perforations of the panel have a relativelysmall size, the correspondence between each spray nozzle and aperforation of the panel is not required in order to obtain asatisfactory mixture.

Advantageously, a water treatment installation according to theinvention comprises a first and a second distribution network of saidpressurised water respectively according to two different distributionflow rate values.

This approach can make it possible to spray pressurised water accordingto a flow rate Q1 delivered by the first network, according to a flowrate Q2 delivered by the second network, and according to a flow rate Q3equal to the sum of flow rates Q1 and Q2 when the two networks areactivated simultaneously. The flow rate can be chosen for exampleaccording to the flow of water to be treated and/or according to itsquality. According to an advantageous characteristic, said nozzle isconnected to said first and second distribution networks.

Such nozzles, also called double nozzles, due to the fact that they areconnected directly to the two networks, can also be used when the plateforming a splash board is or is not implemented. Their use is howeverrecommended when the plate forming a splash board is not implemented andeach of the nozzles extends in the axis of the perforations of thepanel.

According to an alternative, said nozzles belong advantageously to twocategories of nozzles, a first category of nozzles being connected tosaid first network and a second category of nozzles being connected tosaid second network.

Such spray nozzles can be used preferentially when the plate forming asplash board is implemented, or when the perforations of the panel havea diameter of small size, advantageously between two and thirtycentimetres.

According to an advantageous characteristic, said nozzle(s) include twoperforated plates arranged across from one another.

These nozzles include therefore two perforated walls, also calledpressure-reducing walls, which make it possible respectively to subjectthe pressurised water to a first strong pressure reduction then a secondlow pressure reduction making it possible to spray water accompaniedwith micro air bubbles. The spraying furthermore makes it possible toprevent strong shear rates on the spraying stage.

According to a preferred characteristic, said nozzles have a lowerdivergent outline.

The implementation of a lower divergent outline can in particular makeit possible to render the spraying phenomenon reliable.

Advantageously, said divergent outline is flat and forms an angle γ withthe vertical between 0 and 20°.

Preferentially, said divergent outline is curved.

According to a preferred aspect of the invention, the upper part of saidwall separating said mixing zone from said flotation zone has a portioninclined according to an angle α in the direction of said flotationzone.

In this case, the value of said angle α is advantageously between 120°and 175°.

According to another advantageous aspect, said wall separating saidmixing zone of said flotation zone has an upper portion curved in thedirection of said flotation zone.

In this case, said curved portion has preferentially a radius between0.1 and 1 metre.

The implementation of such inclined or curved portions can in particularmake it possible to facilitate the passage of the water from the mixingzone towards the flotation zone.

Advantageously, said flotation zone accommodates a plurality ofpartitions extending substantially vertically above said take-up zone.

The implementation of such partitions makes it possible to fragment theclarified water which flows towards the bottom of the flotation zone andas such to prevent the appearance of the recirculation loop phenomenon.This participates in preventing the clarified water from mixing with thebed of air bubbles whereon are agglomerated particles initiallycontained in the water to be treated.

Preferentially, at least one of said partitions has at least one upperpart inclined according to an angle β or curved.

Preferentially the angle β has a value between 120° and 240°.

These inclined or curved portions can make it possible to improve therecirculation breakage in the clarified-water take-up zone.

Advantageously, said partitions have a height between 30 and 300centimetres. According to another preferred aspect of the invention,said partitions are closer to one another in the vicinity of said wallseparating said mixing zone from said flotation zone.

This can in particular contribute to preventing the formation of inducedrotations of the flow between two plates.

Preferably, said partitions are separated by a distance between 20 and300 centimetres.

Preferentially, said take-up zone accommodates means for taking upclarified water connected to means of collecting clarified water.

According to an advantageous aspect, a water treatment installationaccording to the invention comprises means for producing saidpressurised water.

Preferentially, said means for producing are connected to said means fortaking up clarified water and to a source of air production.

The pressurised water can thus be formed using clarified water availableat the outlet of the installation according to the technique shown here.In an alternative, the pressurised water can also be formed using waterto be treated that is more preferably non-coagulated andnon-flocculated.

Advantageously, a water treatment installation according to theinvention comprises scraping means able to be displaced across from theupper part of said flotation zone.

These scraping means make it possible to remove the beds of air bubblessimply and effectively.

The invention also relates to a flotation water treatment method byflotation which consists in transiting the water into an installationaccording to the technique shown here, and in admitting into said mixingzone an ascending current of said water to be treated through saidperforated panel, and a current of said pressurised water by means ofsaid spray nozzle(s) in such a way as to form air bubbles able to bringparticles in suspension in said water to be treated towards the surfaceof said mixing zone.

According to a preferred aspect, said current of said pressurised wateris initially ascending.

According to another preferred aspect, said current of said pressurisedwater is initially descending.

According to yet another preferred aspect of the technique shown here,said current of said pressurised water is initially horizontal.

Indeed, according to the quality of the water to be treated, more orless resistant flocs can be formed during coagulation-flocculation. Theway the nozzle is provided depends on the resistance of the flocs. Ifthe floc is fragile, the co-current is favoured to create a sufficientrequired shear rate. In the case where the coagulation-flocculationforms highly-resistant flocs, the counter-current is favoured.

Thus, according to whether the panel extends substantially horizontallyor vertically, and that the flocs are fragile or resistant, the nozzlescan be positioned in such a way that the pressurised water is sprayedco-current or counter-current to the water to be treated.

In another alternative, the nozzles can also be installed substantiallyhorizontally when the panel extends substantially horizontally.

Advantageously, a water treatment method by flotation according to theinvention comprises a step of choosing one of said values of said flowrate of distribution of said pressurised water according to the flowrate of said water to be treated and/or of the quality of said water tobe treated.

A method according to the invention can therefore be modulated due tothe fact that it can be adapted to a large number of situations.

According to another advantageous aspect, a water treatment method byflotation according to the invention consists in implementing saidscraping means in order to remove outside of said flotation zone saidparticles agglomerated to said air bubbles.

LIST OF FIGURES

Other characteristics and advantages of the invention shall appear moreclearly when reading the following description of preferred embodiments,provided only for the purposes of information and in a non-limitingmanner, and the annexed drawings, among which:

FIG. 1 shows an installation for water treatment according to prior art;

FIG. 2 shows the speed vectors of the flow of liquid inside theinstallation shown in FIG. 1;

FIG. 3 shows a first embodiment of an installation for water treatmentaccording to the technique shown here, wherein a perforated panelseparates the inlet zone of the water to be treated from the mixingzone;

FIG. 4 shows a partial view of an alternative of the installation inFIG. 3 wherein several spray nozzles are implemented withoutcorrespondence with the perforations of the perforated panel;

FIG. 5 is a schematic view of a spray nozzle able to be connected to twospray networks of pressurised water according to different rates;

FIG. 5 bis shows an alternative of the lower outline that can have anozzle shown in FIG. 5;

FIGS. 6 and 6 bis show two architectures of a distribution network ofpressurised water implementing nozzles such as shown in FIG. 5;

FIG. 7 shows a second embodiment of an installation for water treatmentaccording to the invention that comprises a plate with holes interposedbetween the spray nozzles and the perforated panel;

FIG. 8 is a partial view of an alternative of the installation in FIG.7, wherein several rows of nozzles are implemented;

FIG. 8 bis shows another alternative of a plate forming a splash board;

FIG. 9 shows an example of an architecture of a distribution network ofpressurised water wherein nozzles of a first category are connected to aspray network of pressurised water according to a first flow rate andnozzles of a second category are connected to a spray network accordingto a second flow rate of pressurised water;

FIG. 10 shows the speed vectors of the flow of liquid inside aninstallation according to the technique shown here.

DESCRIPTION OF EMBODIMENTS OF THE TECHNIQUE SHOWN HERE Brief Reminder ofthe Principle of the Technique Shown Here

The main principle of the invention is based on the implementation of aninstallation for water clarification by flotation, which comprises aperforated panel that separates an inlet zone of water to be treatedwhich is coagulated and flocculated beforehand from a mixing zone of thewater to be treated with a pressurised and then depressurised water, themixing zone containing one or several spray nozzles of the pressurisedwater.

The presence of the perforated panel makes it possible to homogenise andto fragment the flow in the mixing zone of the water to be treated. Thisfragmentation makes it possible to homogenise the contact between thewater to be treated and the micro air bubbles formed in the mixing zoneacross the entire horizontal section of the mixing zone. Theimplementation of such a perforated panel makes it thus possible tooptimise the clarification of the water by flotation.

Furthermore, the installation according to the invention furthercomprises a flotation zone accommodating partitions spaced apart fromone another and which extend substantially vertically and in parallel inrelation to one another.

The implementation of such partitions inside the flotation zone makes itpossible to break the lines of the flow of liquid flowing in theflotation zone. This makes it possible to prevent the recirculationphenomenon in particular in the lower part of the flotation zone, i.e.the clarified water from returning in contact with the bed of bubbles tothe surface of the flotation zone. The driving of particles insuspension agglomerated to the air bubbles in the clarified-watertake-up zone can thus be prevented, or at least limited.

The implementation of such partitions contributes to preventing airbubbles from being removed with the clarified water collected, and toconsequently improve the quality of the clarified water collected.

Example of a First Embodiment of a Water Treatment Plant According tothe Technique Shown Here

In reference to FIG. 3, an embodiment of an example of an installationfor water treatment by flotation according to the invention isdescribed.

Such an installation comprises an inlet zone 31 of water to be treated.The water to be treated is coagulated and flocculated beforehand. Tothis effect, a coagulation zone and a flocculation zone are arranged inseries (not shown) upstream of the inlet zone 31.

A mixing zone 32 extends above the inlet zone of water 31. The waterinlet 31 and mixing 32 zones are separated from one another by a panel33 of which at least one portion has perforations 331. Preferentially,the perforations 331 extend over the entire surface of the perforatedpanel 33. The perforations 331 arranged in the panel 33 can for examplehave a circular outline of a magnitude of 15 centimetres in diameter. Inother embodiments, the diameter of the perforations 331 can bedifferent. The diameter can advantageously be between 2 and 50centimetres.

A wall 34 separates the water inlet zones 31 and mixing zones 32 from aflotation zone 35. This wall 34 is substantially vertical in its lowerpart and has in its upper part a portion inclined 341 according to anangle α in the direction of the flotation zone 35. The value of thisangle α is advantageously between 120° and 175°. The implementation ofthis inclined portion 341 makes it possible in particular to facilitatethe passage of the water from the mixing zone towards the flotationzone.

In an alternative of the technique shown here, the inclined portion 341can be replaced by a curved portion 342 (shown as a dashed line in FIG.3) of which the radius can be between 0.1 and 1 metre.

Such a water treatment installation according to the technique shownhere also comprises means for taking up clarified water. These watertake-up means include a chamber 36 of which the upper face 361 isperforated over at least one portion of its surface in such a way toallow the clarified water to penetrate therein. Moreover, the chamber 36is connected to a conduit 37 which extends outside of the flotation zone35 in the direction of a spillway (not shown), or any other means, whichmakes it possible to collect the clarified water obtained after theflotation treatment.

In an alternative of the technique shown here, the perforated chamber 36can be replaced by perforated piping housed in the lower part of theflotation zone 35.

Vertical partitions 39 extend transversally and substantially verticallyin the flotation zone 35. The height of these partitions 39 can bebetween 30 and 300 centimetres. These partitions 39 are solid and can bearranged at regular intervals or not. They can for example be spaced ata distance between 30 and 300 centimetres.

Preferentially, the closer the partitions 39 are to the wall 34, thesmaller the separating distance is. This makes it possible to preventthe appearance of induced rotations 102 of fluid between two plates 39as is shown in FIG. 10.

In other embodiments, the partitions 39 can be perforated. This inparticular has the advantage of improving the distribution of theclarified water over the entire horizontal surface of theclarified-water take-up zone. Moreover, it can be provided that thesepartitions 39 be removable in particular in such a way to facilitate themaintenance of the device according to the technique shown here.Furthermore, these partitions 39 are preferentially made of steel of thestainless type. In alternatives, they can be made of materials of theplastic type. This can be particularly advantageous when treating seawater.

In alternatives of the technique shown here, the partitions 39 can alsohave a portion 391 that is inclined in relation to the vertical of anangle β of which value can be between 120 and 240° such as is shown as adashed line in FIG. 3. They can also be inclined over their entirelength. In another alternative, the partitions 39 can have a curvedportion 392 (shown as a dashed line) in the direction of the wall 34 ornot. The implementation of these inclined 391 or curved 392 portionsmakes it possible to improve the recirculation breakage in theclarified-water take-up zone.

Moreover, the mixing zone 32 accommodates at least one spray nozzle 40of a pressurised water, placed in the vicinity of the perforated panel33.

In this embodiment, nozzles 40 are placed in the axis of eachperforation 331 of the panel 33 as is shown in FIG. 3. The diameter ofthe perforations 331 preferentially ranges between 5 and 50 centimetres.This makes it possible to provide an optimal mixture between the flowsof water to be treated and pressurised water.

However, in an alternative of this embodiment wherein the perforations331 arranged in the perforated panel 33 have a small diameter,advantageously between 2 and 30 centimetres, the correspondence betweeneach nozzle and a perforation 331 is not required as shown in FIG. 4.

As shall be explained in more detail in what follows, these spraynozzles 40 make it possible to generate an initially descending currentof pressurised and then depressurised water in the mixing chamber 32. Inthis case, the pressurised water is sprayed in the mixing chamber 32 atcounter-current in relation to the water to be treated.

In an alternative of this embodiment, the spray nozzle(s) 40 can bearranged in such a way to generate an initially ascending current ofpressurised water inside the mixing zone. In this case, the pressurisedwater is sprayed in the mixing chamber at co-current in relation to thewater to be treated.

These spray nozzles 40 are connected to means of producing pressurisedwater 42 by the intermediary of pipes 41. The means of producingpressurised water 42 are connected to a pressurisation balloon (notshown) provided with one or several aeroejectors which provide theair-water mixture. These means of producing pressurised water areconnected on the one hand to the conduit 37 wherein clarified waterflows by a tube 43, and on the other hand to a source of air production44. The pressurised water, of which the pressure is advantageouslybetween 3 and 8 bars, is thus produced using a portion of the clarifiedwater collected and air.

As shall be explained in more detail in what follows, several means ofproducing pressurised water can be placed in parallel in such a way toallow for the spraying of the pressurised water according to differentrates.

In relation with FIG. 5 an example of spray nozzle 40 is described.

Note that the operating principle of these spray nozzles 40, whichconsists of a double pressure reduction, is similar to that of sprayersof the WRC type. However, and such as shall appear more clearly in whatfollows, several characteristics differentiate the spray nozzles 40 fromsprayers of the WRC type. The spray nozzles 40 are connected to twoinlets of pressurised water flowing at different flow rates Q1 and Q2.They thus allow for the spraying of pressurised water according to threeflow rates: Q1, Q2, Q1+Q2.

Such as is shown, such spray nozzles 40 have a main hollow body 51 ofwhich one end is provided with a first perforated pressure-reducing wall52 and with a second perforated pressure reducing wall 53 placed acrossfrom one another and parallel in relation to one another thus creatingan intermediary chamber. The perforations arranged in the firstpressure-reducing wall 52 and in the second pressure reducing wall 53are distributed substantially uniformly at their surface. The density ofperforations of the first pressure-reducing wall 52 is less than thedensity of perforations of the second pressure reducing wall 53.Moreover, the surface of the perforations arranged in the firstpressure-reducing wall 52 is greater than the surface of theperforations arranged in the second pressure reducing wall 53. Thevalues of the diameters of these perforations are between 1 and 15millimetres.

Moreover, the lower end of the main body 51 forms an angle γ in relationto the vertical. The value of this angle γ is between 0 and 20°.According to one alternative of the technique shown here, shown in FIG.5 bis, the lower part of the main body 51 is curved. The fact that themain body 51 has a divergent form makes it possible to facilitate thespraying.

The main body 51 houses a secondary hollow body 54. This secondaryhollow body 54 is able to be crossed by a first flow of pressurisedwater of flow rate Q1, while the main hollow body 51 is able to becrossed by a second flux of pressurised water of flow rate Q2 of apreferably higher value. This flow rate Q2 can also be of a lesser valuein an alternative.

In this embodiment, each spray nozzle 40 is therefore connected to twodistribution networks of pressurised water able to deliver respectivelypressurised water at flow rate Q1 and at flow rate Q2. The means ofproducing pressurised water 42 are thus split (not shown) in such a wayto make it possible to provide three flow rates Q1, Q2 and Q1+Q2 ofpressurised water.

As shown in particular in FIGS. 3, 4, 6 and 6 bis, several rows 45 of aplurality of spray nozzles 40 can be arranged in parallel.

FIG. 6 is a diagram showing an example of architecture of a distributionnetwork of pressurised water implementing two rows 45 of spray nozzles40.

Such a network comprises two distribution networks of a flow rate Q1 ofpressurised water and two distribution networks of a flow rate Q2 ofpressurised water in such a way to implement two rows of spray nozzles.

As shown, each spray nozzle 40 of each row 45 is connected to the firstdistribution network of a flow rate Q1 of pressurised water by means ofthe pipe 41 and to the second distribution network of a flow rate Q2 ofpressurised water by means of a pipe 41′.

One alternative, shown in FIG. 6 bis, consists in implementing two rowsof spray nozzles 40 without splitting the distribution networks Q1 andQ2.

A water treatment installation according to the technique shown herefurther comprises a scraper (not shown). As shall be explained in moredetail in what follows, such a scraper makes it possible to remove thesludge, constituted of matter in suspension, organic matter, algaeinitially present in the raw water, floating in the upper part of themixing 32 and flotation 35 zones, as well as the air bubbles introducesinto the structure outside of the flotation zone (arrow 1) in the meansof recovering 46.

Example of a Second Embodiment of a Water Treatment Plant According tothe Technique Shown Here

In reference to FIGS. 7 to 9 a second embodiment of a water treatmentinstallation according to the technique shown here is described.

In this second embodiment, the water treatment installation has a largenumber of characteristics that are common with those of the installationaccording to the first embodiment described hereinabove. Only thedifferences between the first and second embodiment shall be describedhere.

As shown in FIG. 7, a perforated plate 71, housed inside the mixing zone32 downstream of the perforated panel 33, is implemented in this secondembodiment. This perforated plate 71 is arranged in such a way that theinterstices 711 that are arranged therein are across from solid parts ofthe perforated panel 33. In other words, the interstices 711 and theperforations 331 are not aligned, in such a way as to form baffles, suchas is clearly shown in FIGS. 7 and 8.

The interstices crossing the perforated plate 71 can have a diameterbetween 2 and 50 centimetres. Moreover, the perforated panel 33 and theperforated plate 71 are advantageously separated by a distance between ⅓of the diameter of the interstices 711 and 3 times the diameter of theinterstices 711.

One or several spray nozzles 40 can be implemented in this secondembodiment. Each spray nozzle 40 must not necessarily be placed in theaxis of an interstice 711.

In the same way as in the embodiment described hereinabove, analternative of this embodiment can consist in implementing several rows45 of spray nozzles 40, such as is shown in FIG. 8.

The spray nozzles implemented in this second embodiment can be similarto the spray nozzles 40 described hereinabove in relation with FIGS. 5and 6.

In an alternative of this second embodiment, shown in FIG. 9, the spraynozzles are different from the spray nozzles 40 described hereinabove inthat each of them is not connected to the first spraying network ofpressurised water at a flow rate Q1 and to the second spraying networkof pressurised water at a flow rate Q2. On the contrary, the spraynozzles implemented in this alternative of the second embodiment areseparated into two categories:

-   -   spray nozzles 91 of a first category are each connected to the        spray network of pressurised water at a flow rate Q1;    -   spray nozzles 92 of a second category are each connected to the        spray network of pressurised water at a flow rate Q2.

These spray nozzles 91 and 92 can for example be of the WRC type or anyother type in accordance with the bubbling principle.

In another alternative, the nozzles 40 are all identical and spray at asingle flow rate.

In an alternative of this embodiment shown in FIG. 8 bis, the perforatedplate can have two types of interstices: basic interstices and refininginterstices 712.

The basic interstices are composed of the interstices 711 arranged insuch a way that the perforated plate 71 comprises a splash board. Therefining interstices 712 are arranged in the solid parts joining basicinterstices 711 of the perforated plate 71. The implementation of theserefining interstices 712 makes it possible to optimise thehomogenisation of the water flow to be treated entering into the mixingzone 32.

The diameters of the basic interstices 711 and refining interstices 712are chosen in such a way that the flow rate crossing the basicinterstices 711 is equal to the flow rate crossing the refininginterstices 712.

Water Treatment Method by Flotation According to the Technique ShownHere

A flotation water treatment method according to the technique shown hereshall now be described.

Such a method consists in transiting the water to be treated into awater treatment installation according to one or the other of theembodiments described hereinabove.

The water to be treated which is coagulated and flocculated beforehandis directed towards the inlet zone of water 31. The water to be treatedis then injected according to an ascending current into the mixing zone32 by passing through the perforations 331 of the perforated panel 33.

At the same time, pressurised and then depressurised water is injectedinto the mixing zone 32, at counter-current of the ascending current ofthe water to be treated, by means of spray nozzles 40. As indicatedhereinabove, it can be provided that the pressurised water be injectedinto the mixing zone at co-current.

The pressurised water is obtained, after activation of the means forproducing pressurised water 42, using a portion of the clarified waterwhich is removed from the flotation zone 35 and air coming from thesource of air 44.

The pressurised water flows in the conduit 41 to the spray nozzles 40.It first crosses the first pressure-reducing wall 52. The pressurisedwater then undergoes a strong loss of pressure and expands. Thepressurised and then depressurised water then crosses the secondpressure reducing wall 53 and undergoes a slight loss of pressureallowing it to be sprayed. This spraying phenomenon participates inpreventing the strong shear rates on the spraying stage.

The spraying of the pressurised and then depressurised water into themixing zone 32 is accompanied with the formation of micro air bubblesdistributed homogenously over the entire horizontal section of themixing zone 32.

The fact that the water to be treated is injected into the mixing zone32 by crossing the perforated panel 33 makes it possible to homogeniseand to fragment its flow by preventing the formation of short circuits,recirculation zones and dead zones. In other terms, the implementationof the perforated panel 33 makes it possible to provide homogenouscontact and across the entire horizontal section of the mixing zone 32of the water to be treated and of the micro air bubbles.

The homogenisation of the contact of the water to be treated and themicro air bubbles can be improved further when the plate with holes 71is interposed between the perforated panel 33 and the spray nozzles.

Thus, the combination of the homogenisation of the flow of water to betreated, through the presence of the perforated panel, with thearrangement of the spray nozzles across from each perforation of theperforated panel, and/or with the implementation of the perforated plateforming a splash board, makes it possible to provide an optimal mixturebetween the water to be treated and the pressurised water.

The micro air bubbles have aim to bring towards the surface of themixing zone 32 and of the flotation zone 35 all of the particles insuspension in the water to be treated. Thus, the fact that the contactbetween the water to be treated and the micro air bubbles is homogenousmakes it possible to optimise the clarification of the water to betreated and to substantially improve the effectiveness of the treatmentof the water by flotation.

The mixture constituted of the micro air bubbles whereon areagglomerated the particles that were initially in suspension in thewater to be treated are then displaced towards the upper part of theflotation zone 35 such as is shown by the arrow J. This mixture can thenbe removed outside of the flotation zone 35 by means of the scraper (notshown) which makes it possible to scrape the surface of the flotationzone 35 in order to direct the sludge produced as well as air bubbles inthe direction of the means of recovering 46 such as is shown by thearrow I.

The clarified water thus flows in the direction of the lower part of theflotation zone 35 which accommodates the chamber 36 and meets thepartitions 39. The flow of the clarified water is fragmented by thesepartitions 39.

The implementation of these partitions 39, due to the fact that theyallow the flow of clarified water to be fragmented inside the flotationzone 35, makes it possible to prevent the appearance of a recirculationloop in the vicinity of the clarified-water take-up zone.

This is clearly shown in FIG. 10 which shows the speed vectors of theflow of liquid 101 inside the flotation zone 35.

A comparison of FIGS. 2 and 10, which show respectively the speedvectors of the liquid inside a flotation zone of an installationaccording to prior art and of an installation according to the techniqueshown here, makes it possible to better apprehend the modifications ofthe flow of liquid which result from the implementation of partitions 39in the flotation zone 35.

It is clearly shown in FIG. 2 that the speed vectors 21 are concentratedinto a vortex at the centre of the flotation zone. This vortex creates arecirculation loop phenomenon and directs the clarified water in thedirection of the upper part of the flotation zone, portion wherein itmixes with the bed of micro bubbles.

On the contrary, it appears clearly in FIG. 10 that the speed vectors ofthe liquid break against the partitions 39 and that the speed vectorslocated between these partitions 39 are not disturbed, i.e. they do notrise in the direction of the upper part of the flotation zone.

The implementation of such partitions 39 thus makes it possible toprevent the recirculation loop phenomenon in the lower part of theflotation zone, wherein is located the chamber 36 allowing for thetaking up of the clarified water, and therefore to prevent, or at thevery least limit, the departure of micro air bubbles with the clarifiedwater.

The implementation of partitions 39 makes it possible to prevent thedeparture of bubbles and sludge towards the taking up in of clarifiedwater and therefore to prevent the clarified water collected from beingdirtied by micro air bubbles loaded with particles.

The technique according to the invention therefore makes it possible tooptimise the clarification of the water by flotation and to improve thequality of the clarified water collected at the end of the flotationtreatment.

Moreover, the method according to the invention can also include a stepconsisting in choosing the value of the flow rate of the pressurisedwater injected into the mixing zone. The choice of the value of the flowrate of the pressurised water can be linked to the flow rate of thewater to be treated and/or to the quality of the water to be treated.Indeed, if the flow rate of the water to be treated varies inproportions from 1 to 4,and/or if the quality of the water to be treatedchanges, it is interesting, in particular from an economic standpoint,to be able to vary in the same proportions the flow rate of thepressurised water.

As such, when the flow rate of the water to be treated is rather lowand/or the quality of the water to be treated is relatively good, themeans of producing pressurised water according to the flow rate Q1 willbe activated.

When the flow rate of the water to be treated increases and/or when thequality of the water to be treated is degraded, the means of producingpressurised water according to the flow rate Q2 will be activated, orall of the means of producing can be implemented so as to provide a flowrate equal to the sum of Q1 and Q2.

1-34. (canceled)
 35. A flotation water treatment system for treatingwater, comprising: an inlet zone for receiving the water to be treated;a mixing zone for receiving water from the inlet zone; a flotation zonefor receiving water from the mixing zone; a clarified water collectionarea for receiving water clarified in the flotation zone; one or morespray nozzles disposed in the mixing zone for injecting pressurizedwater into the mixing zone and generating air bubbles in the mixing zonesuch that the air bubbles are mixed with the water to be treated; aperforated panel separating the inlet zone and mixing zone and includingan array of openings through which water to be treated passes as thewater to be treated moves from the inlet zone to the mixing zone; andwherein the openings in the perforated panel give rise to a homogenousmixture of the water to be treated and the air bubbles that result fromthe pressurized water being injected into the mixing zone by the one ormore spray nozzles.
 36. The water treatment system of claim 35 whereinat least a portion of the mixing zone is disposed over the inlet zoneand wherein the perforated panel extends generally horizontally betweenthe mixing zone and the inlet zone.
 37. The water treatment system ofclaim 35 wherein the perforated panel forms a first perforated panel andwherein there is provided a second perforated panel that includes anarray of openings therein, and wherein the second perforated panel isdisposed adjacent the first perforated panel, and wherein the first andsecond perforated panels separate the inlet zone from the mixing zone.38. The water treatment system of claim 37 wherein at least some of thearray of openings in the second perforated panel are not aligned withthe array of openings in the first perforated panel.
 39. The watertreatment system of claim 38 wherein the second perforated panel isdisposed closer to the one or more spray nozzles than the firstperforated panel and wherein the second perforated panel forms a splashboard.
 40. The water treatment system of claim 38 wherein at least someof the openings in the second perforated panel are at least partiallyaligned with openings in the first perforated panel.
 41. The watertreatment system of claim 35 including a network for directingpressurized water to the one or more spray nozzles, and where thenetwork includes a first distribution network for directing pressurizedwater to the one or more spray nozzles at a first flow rate, and asecond distribution network for directing pressurized water to the oneor more spray nozzles at a second flow rate.
 42. The water treatmentsystem of claim 41 wherein the one or more spray nozzles includes aplurality of spray nozzles including nozzles of a first type and nozzlesof a second type and wherein the nozzles of the first type areoperatively connected to the first distribution network and the nozzlesof the second type are operatively connected to the second distributionnetwork.
 43. The water treatment system of claim 35 wherein each of theone or more spray nozzles includes two perforated plates through whichthe water-air mixture passes.
 44. The water treatment system of claim 35wherein each of the one or more spray nozzles includes an outlet that isflared outwardly.
 45. The water treatment system of claim 44 wherein theoutlet of each spray nozzle is curved.
 46. The water treatment system ofclaim 35 including a wall that extends generally between the mixing zoneand the flotation zone and wherein the wall includes an upper portionthat is turned and directed towards the flotation zone.
 47. The watertreatment system of claim 46 wherein the wall separating the mixing zoneand the flotation zone includes an upper potion disposed at an angle ofapproximately 120° to approximately 175°.
 48. The water treatment systemof claim 46 wherein the wall separating the mixing zone and theflotation zone includes an upper portion curved in the direction of theflotation zone.
 49. The water treatment system of claim 35 including aclarified water zone disposed in a lower part of the flotation zone; andwhere the flotation zone includes a plurality of partitions that arespaced apart and extend generally vertically above the clarified waterzone.
 50. The water treatment system of claim 49 wherein the partitionsare separated by a distance of approximately 20 to approximately 300 cm.51. The water treatment system of claim 35 including means for producingpressurized water that is directed to the one or more spray nozzles. 52.The water treatment system of claim 35 wherein the system includes aclarified water collection area disposed adjacent the flotation zone andwherein there is provided means for pressurizing the water mixturedirected to the one or more spray nozzles and wherein the means forpressurizing the water is operatively connected to the clarified watercollection area such that clarified water from the flotation zone can bedirected under pressure to the spray nozzles.
 53. The water treatmentsystem of claim 35 including a plurality of spaced apart partitionsdisposed over the flotation zone and over the clarified water collectionarea.
 54. The water treatment system of claim 53 wherein selectedpartitions in the flotation zone include a lower section that isdisposed in a vertical orientation and an upper section that extendsfrom the lower section at an angle or which is generally curved andextends from the lower section.
 55. The water treatment system of claim35 including a pump for pressurizing water and directing the pressurizedwater to the one or more spray nozzles disposed in the mixing zone. 56.The water treatment system of claim 55 wherein the pump is operative topump water collected in the clarified water collection area through oneor more conduits to the one or more spray nozzles.
 57. The watertreatment system of claim 35 where the system includes a plurality ofspray nozzles and wherein the spray nozzles are disposed adjacent theperforated panel separating the inlet zone from the mixing zone.
 58. Thewater treatment system of claim 57 wherein each spray nozzle includes apair of spaced apart perforated structures through which pressurizedwater flows when the spray nozzles inject the pressurized water into themixing zone.
 59. The water treatment system of claim 35 wherein each ofthe one or more spray nozzles includes two separate inlets for receivingtwo different pressurized streams of water; and wherein the watertreatment system includes a pump for directing two separate pressurizedstreams of water to respective spray nozzles.
 60. A method removingsuspended particles in water through a flotation process, the methodcomprising: directing the water to be treated having the suspendedparticles into an inlet area; directing the water to be treated from theinlet area into a mixing zone; pressuring the water and directing thepressurized water to one or more spray nozzles disposed in the mixingzone and ejecting the pressurized water from the one or more spraynozzles into the mixing zone causing air bubbles to be formed and mixedwith the water to be treated in the mixing zone; directing the water inthe mixing zone along with the suspended particles to a flotation zonewhere the air bubbles are effective to cause the suspended particles tofloat in an upper level of the flotation zone where the suspendedparticles can be removed; collecting clarified water in a clarifiedwater collection area; and providing a generally homogeneous mixture ofthe water and the pressurized water in the mixing zone by directing thewater to be treated from the inlet area through a perforated platehaving an array of openings therein which separates the inlet area fromthe mixing zone such that water to be treated moving from the inlet areato the mixing zone passes through the array of openings in theperforated plate, resulting in a generally homogeneous mix of the waterto be treated with the pressurized water in the mixing zone.
 61. Themethod of claim 60, wherein substantially all of the water to be treatedis constrained to move through the perforated plate having the array ofopenings as the water moves from the inlet area to the mixing zone. 62.The method of claim 60 including orienting the one or more spray nozzlesin the mixing zone such that the ejected pressurized water from the oneor more spray nozzles is directed counter or co-currently with respectto the water to be treated that moves through the mixing zone.
 63. Themethod claim 60 wherein there is provided a clarified water take-up zoneabout the lower portion of the flotation zone, wherein the methodincludes generally preventing the occurrence of a recirculationphenomenon in the clarified water take-up zone.
 64. The method of claim63 including partitioning the clarified water take-up zone so as togenerally prevent the occurrence of the recirculation phenomenon. 65.The method of claim 60 wherein at least a portion of the pressurizedwater is sourced from the clarified water collection area.
 66. Themethod of claim 60 wherein each of the one or more spray nozzlesincludes two inlets and the method includes directing one stream ofpressurized water to one inlet and directing another stream ofpressurized water to the other inlet, and wherein the flow rates of thetwo pressurized streams are different.
 67. The method of 60 wherein thepressurized water is ejected in the mixing zone such that the ejectedpressurized water is initially ascending.
 68. The method of 60 whereinthe pressurized water is ejected in the mixing zone such that theejected pressurized water is initially descending.
 69. The method ofclaim 60 wherein the mixing zone is disposed over the inlet area, andwherein the perforated plate is generally horizontally disposed betweenthe inlet area and the mixing zone; wherein there is provided apartition that generally separates the mixing zone from the flotationzone; and wherein the clarified water collection area is disposed belowa substantial portion of the flotation zone.